"We're just kind of floating around offensively. We've got guys who can hit, but they're not putting anything together and it's kind of frustrating right now for everyone involved," Twins manager Ron Gardenhire said.

Iwakuma (5-3) gave up one hit and one unearned run over six innings in another strong start for the rookie from Japan. The right-hander struck out four and helped send the Twins to their 16th defeat in their last 19 games despite four walks, a hit batsman and a wild pitch.

The Twins had one of baseball's most productive offenses in June and July, but the end of the summer has brought the dog days for their bats, too.

"You might see one or two guys go into a little bit of a funk, but right now we're inconsistent pretty much up and down the lineup," Gardenhire said.

The announced attendance was 29,854, the first sub-30,000 crowd to watch the Twins since Target Field opened in 2010.

Ackley's drive off a fastball from Scott Diamond (10-6) into the flower bed above right-center field followed consecutive singles by Trayvon Robinson and Brendan Ryan to start the fifth. Diamond gave up more than three runs for the first time in seven starts since July 21, but his survival was the one bright spot of the night. Diamond, whose appeal of a six-game suspension meted out by Major League Baseball last week is still pending, lasted only 2 1-3 innings in his last turn. He was ejected for throwing a pitch behind Rangers All-Star Josh Hamilton in Texas.

This time, Diamond completed seven innings with seven hits and one walk while striking out two despite allowing five runs. The left-hander gave up a double to Ryan and walked Franklin Gutierrez with two outs in the third before Kyle Seager's two-run double put the Mariners on the board. Seager leads the majors with 43 two-out RBIs.

"That's been my goal every game, to try to go as deep as I can, at least seven," Diamond said. "Even though the outcome wasn't so great, I've got to take it as a positive."

The Mariners, who began the day nine games behind in the AL wild-card race, have won 12 of their last 16 games overall and seven straight against the Twins.

After Ryan Doumit's RBI double off Charlie Furbush, Tom Wilhelmsen got the last out of the ninth inning for his 20th save in 23 attempts.

With his unorthodox, halting windup and the exaggerated kick of his right leg before he releases the ball, Iwakuma had the Twins off balance all game. Ben Revere drew a leadoff walk but was immediately erased by a groundball double play, and Robinson made a tricky catch of a long foul ball by Joe Mauer down the left-field line by slamming into the wall and plucking the ball out of the airspace above the seats.

Iwakuma is 4-1 with a 1.99 ERA in his last eight starts. He allowed a run before he surrendered a hit, when consecutive walks to Jamey Carroll and Pedro Florimon set up Revere for a sacrifice fly. Carroll moved up on a wild pitch, and both runners advanced on a passed ball by Miguel Olivo. Not until one out into the fifth did the Twins get a hit, a single by Carroll.

"It's been a struggle. On offense we're not doing what we feel like we're capable of," Carroll said, adding: "We didn't really put up any threats whatsoever. It's frustrating. Obviously it's not what we want to do or where we want to be, especially this time of year."

NOTES: OF Denard Span was scratched from the Twins' lineup two hours before the game after complaining of more soreness around his collarbone. He has had discomfort in that area since diving for a ball and landing hard on Aug. 12, playing in only four of the past 15 games. Revere moved from RF to CF and from second to first in the order, and Darin Mastroianni filled in behind Revere, who made a sliding shoestring catch to take a hit from Robinson in the third. Span was set for an MRI on his shoulder on Wednesday. ... The Mariners have homered in 11 straight games. Justin Morneau has the only home run for the Twins in their last 11 games.

Copyright 2012 by The Associated Press. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.